1. Field of the Invention
The present invention relates generally to magnetic recording disks and methods for their preparation. In particular, the invention relates to the formation of a protective coating over the surface of the magnetic recording disk.
Hard magnetic recording disks comprise a rigid disk substrate, such as aluminum coated with a nickel-phosphorus underlayer, having a thin film of a ferromagnetic composition, such as a magnetic oxide or magnetic alloy, formed thereover. In order to improve the mechanical properties of the disk, other layers may be formed over the ferromagnetic film, typically protective layers and lubricating layers.
Hard disk memory storage devices operate by rapidly rotating the disk while maintaining a magnetic transducer as close to the magnetic (recording) surface of the disk as possible, typically being spaced less than one micron from the disk surface. For reasons best explained elsewhere, such close proximity increases the information storage density on the disk. As a result of the close spacing, as well as head contact which occurs during the starting and stopping of the disk drive, it is desirable that the disks possess a hard protective coating over the recording surface. It is particularly desirable that the protective barrier be lubricious in nature in order to reduce friction between the head and the disk when contact occurs. In addition, because of the propensity for corrosion of magnetic alloys, the protective coating should also provide a high degree of corrosion protection (i.e., passivity) and exhibit low porosity.
Heretofore, such protective layers have generally been formed either from a sputtered carbon or metal layer (see, U.S. Pat. Nos. 4,277,540; 4,411,963; 4,503,125; and U.S. Pat. No. Re. 32,464), or from spin-coated silicon dioxide (Yanagisaw (1985) Tribology and Mechanics of Magnetic Storage Systems 2:21-26 and Suganuma et al. (1982) IEEE Trans. MAG.-18:1212-1217).
Although generally successful, both the sputter deposited layers and the spin-coated silicon dioxide layers suffer from certain drawbacks. In particular, sputter deposition requires a significant capital expenditure which reduces the economic attractiveness of the procedure.
While the spin coating of a silicon dioxide layer is more economic than sputter coating of a carbon or metal layer, the conversion of the silicon hydrate to an oxide form, as taught in the cited references, requires a relatively high temperature treatment. Such high temperature treatment can have an adverse effect on the nickel phosphorus underlayer.
For these reasons, it would be desirable to provide alternate materials and methods for preparing protective layers on hard magnetic recording disks. In particular, it would be desirable that the alternate materials be applied under less rigorous conditions than the spin-coated silicon dioxide layers of the prior art and be applied less expensively and with improved corrosion protection than the sputter-deposited films of the prior art.
2. DESCRIPTION OF THE BACKGROUND ART
Thomas (1986) Optics News, August, pp. 18-22, describes the preparation of optical coatings where a metal alkoxide is applied to an optical surface and converted to the corresponding metal oxide by solvent evaporation. U.S. Pat. No. 3,847,583 describes how alkali oxides and alkaline earth oxides may be incorporated into metal oxide films of the type described by Thomas (1986). Arfsten (1984) J. Non-crystalline Solids 63:243-249 and Sakka et al. (1984) J. Non-crystalline Solids 63:223-235 describe various applications of the conversion of metal alkoxides to metal oxides. Murozono (1982) Jap. J. Appl. Phys. 21:137-141, describe the deposition of titanium dioxide coatings on solar cells by heat treating organo-titanium compounds applied to the solar cell by spinning.